The present invention relates to a liquid crystal display apparatus and, more particularly, to an improvement in a laser-addressed liquid crystal display apparatus.
In parallel with the improvements in the capacity and function of a computer, there is an increasing demand for a terminal which is furnished with a higher resolution display apparatus. Particularly, in the art of computer-aided image processing, newspaper editing and LSI designing, it is desired to design the display apparatus accurately and even locally rewritable.
Difficulty is experienced, however, in increasing the resolution of a cathode ray tube (CRT) beyond 2,000 lines. A display apparatus employing a storage tube is inherently low in the available brightness of a screen, incapable of local erase and, moreover, disproportionate in cost.
What is considered promising recently for the resolution of more than 2,000 lines is a display apparatus in which a liquid crystal substance is thermally addressed by a beam of coherent laser light. For details of such a display apparatus, reference may be made to the paper entitled 37 Laser-Addressed Liquid Crystal Projection Displays" in 37 Proceeding of the S.I.D.", pp. 1-7, 1978. In this prior art display apparatus, a given voltage is applied to the whole surface of a smectic liquid crystal cell to cause the liquid crystal molecules into alignment with the electric field and thereby make the substance transparent. A laser beam selectively addresses the so conditioned liquid crystal cell so that a scattering state is locally developed in the substance (where the substrate is struck by the beam) and stored accordingly. The scattered state of the cell is caused by the thermal energy of the laser beam. Also discussed in this paper is the technique of laser-addressing the liquid crystal cell while applying a relatively low voltage thereto, whereby it is possible to locally erase data (local erase mode). The display is combined with a projection system to display data in black on a white background, i.e., in the negative mode. However, this type of display is sometimes less agreeable to spectators in some applications.
For multicolor display, a plurality of liquid crystal light valves are used to display and combine images which individually correspond to different colors. In this instance, should the light valves be of the positive mode type, it would be difficult to display color data on a black background.
Meanwhile, to display white data on a black background i.e., positive mode display, an apparatus has been proposed which scans the whole surface of a smectic liquid crystal material to set up a scattering state by a laser beam and then focuses a laser beam onto the material in the local erase mode. Still, this kind of positive mode display is impractical in view of the fact that the laser beam scanning at the present stage of development requires as long a time period as several seconds for displaying one frame.